Systemic lupus erythematosus (SLE) is a prototypic multi-systemic autoimmune disease, which results in significant morbidity and mortality. While the pathogenesis of SLE remains unknown, several alternative hypotheses have been proposed. B and T cell immunity to the Sm antigen is a characteristic feature of SLE. We have previously shown that T cell immunity against Sm can be detected in SLE patients and that T and B cell immunity against Sm are linked in vivo. We have also shown that Sm-reactive T cells have a T helper cell phenotype, produce cytokines important in B cell help and differentiation, and that T cell receptor (TCR) third complementarity determining region (CDR3) usage by Sm-reactive T cells is highly restricted. Recent work from our laboratory has led to the hypothesis that SLE is a T cell dependent, antigen-driven immune process, where T cell immunity is directed against a highly-restricted set of self-peptides, encoded within the conserved Sm motif 1 & 2 on Sm proteins B1, B2, D1, D2, D3, E, F and G. In support of this hypothesis, we have recently identified and begun to characterize the cellular and molecular basis of immunity against Sm. To test this hypothesis we have designed [3] Specific Aims Aim [1]. Define the molecular requirements for TCR activation by Sm-dominant peptides. Aim [2]. Determine the spectrum of peptide ligands that can activate the TCR from Sm-reactive T cell clones using positional scanning synthetic combinatorial libraries (PS-SCL) and single amino acid modified peptide analogues. Aim [3]. Enumerate Sm-reactive T cells and compare these to disease activity in SLE. The proposed research is designed to accomplish the four stated aims and will address the hypothesis that SLE is a T cell dependent, antigen-driven immune process directed against the Sm motifs on Sm polypeptide antigens. In Aim [1] TCRA/B gene transfectants will be constructed in the J.RT3-T3.5 cell line; these will be used to generate a series of lines with alanine substituted TCR CDR3 for comparison to the parental lines. These cell lines will help define the molecular requirement of the TCR for ligand recognition. Aim [2] will define the ligands that stimulate Sm-reactive TCR using synthetic combinatorial libraries and single amino acid substituted peptides. Finally, intracellular IFN-gamma [and IL-4] will be measured in a prospective clinical study as Aim [3]. Stimulation of PBMC by Sm dominant peptides will determine whether the number of IFN-gamma positive cells from peripheral blood correlates with other established measures of disease activity.